During the 1996/7 season, three field trials were undertaken to assess the effect of different formulations on field efficacy of Metarhizium flavoviride (isolate FI-985) for control of Australia's most serious grasshopper pest, Phaulacridium vittatum (Sjostedt), known as the wingless grasshopper. In the first trial, a mineral oil (Propar 12), a vegetable oil (canola), and a water-based spray were compared with a rice/conidia bait. All were applied at 4 x 1012conidia/ha. Live grasshopper samples were collected 4 days after spraying and incubated in a glasshouse at 25-280C for a further 10 days. The two oil formulations were very effective, giving over 90% mortality, while the water (72%) and the rice bait (38%) did not perform satisfactorily. A second experiment compared the Propar 12 mineral oil with another vegetable oil, soybean, on 3-5 ha plots at two sites. In this trial, a dose of 4 x 10 12conidia/ha was used in an oil/water emulsion sprayed at 31 L/ha. Similar results were obtained at the two sites, with both oils giving over 95% control based on glasshouse incubation of field treated grasshoppers. Propar 12 was marginally superior in speed of kill and in the persistence of the conidia on the vegetation. However, few conidia survived more than 4 days in either oil. Field populations were reduced significantly in all treated plots 18-21 days after spraying. In the third trial, the persistence of Propar 12 and soybean oil formulations was compared at a high dose of 2 x 10 13 conidia/ha. The Propar 12 formulation was more persistent, with the spray deposit still giving 37% infection after 6 days exposure. In contrast, the soybean formulation gave 12% infection after 6 days. It is concluded that both Propar 12 and soybean oil are effective formulations and can be used as both ULV and oil/ water emulsion.